RAIM (Receiver Autonomous Integrity Monitoring) provides integrity monitoring of a GNSS (Global Navigation Satellite System) to GNSS receivers. RAIM algorithms process GNSS signals and are based on statistical methods, with which faulty GNSS signals can be detected. Enhanced RAIM algorithms allow not only fault detection (FD) of any received GNSS signal, but also exclusion of a GNSS signal being detected as faulty from positioning, thus allowing a continuous operation of a GNSS receiver. This is known as fault detection and exclusion (FDE).
RAIM is important for safety-critical applications such as in aviation navigation. GNSS based navigation in aviation is until now not standardized by the ICAO (International Civil Aviation Organization). However, the maximum allowable offsets, bends, and errors during precision landing of an airplane are categorized in three different categories CAT-I, CAT-II, and CAT-III, wherein CAT-III contains the smallest allowable offsets, bends, and errors.